1. Field of the Invention
The present invention generally relates to gas lift devices for rejuvenating low-producing or non-productive oil or gas wells, and more particularly to improvements in the design and construction of bypass plungers.
2. Background of the Invention and Description of the Prior Art
A conventional bypass plunger is a device that is configured to freely descend and ascend within a well tubing, typically to restore production to a well having insufficient pressure to lift the fluids to the surface. It may include a self-contained valve—also called a “dart” or a “dart valve” in some embodiments—to control the descent and ascent. Typically the valve is opened to permit fluids in the well to flow through the valve and passages in the plunger body as the plunger descends through the well. Upon reaching the bottom of the well, the valve is closed, converting the plunger into a piston by blocking the passages that allow fluids to flow through the plunger. With the plunger converted to a piston, blocking the upward flow of fluids or gas, the residual pressures in the well increase enough to lift the plunger and the volume of fluid above it toward the surface. Upon reaching the surface, the fluid is passed through a conduit for recovery, the valve in the plunger is opened by a striker mechanism, and the plunger descends to repeat the cycle.
In a typical bypass plunger the valve is similar to a poppet valve, with a valve head attached to one end of a valve stem, such as an intake valve of an internal combustion engine. The valve head, at the inward end of the stem, may be configured to contact a valve seat within the hollow body of the plunger. The stem protrudes outward of the bottom end of the plunger body. A clutch device may surround the stem of the valve to retard and control the motion of the stem and thereby maintain the valve in an open or closed configuration during respectively the descent or ascent of the plunger. The valve thus moves between these two positions to open the flow passages at the surface when the plunger contacts the striker mechanism, and to close the bypass passages at the bottom of the well when the stem strikes the bottom, usually at a bumper device positioned at the bottom of the well. Descent of the plunger is controlled by gravity, which pulls it toward the bottom of the well when the valve is open.
This valve or “dart” may be held open or closed by the clutch—typically a device that exerts circumferential friction around the valve stem. The dart may be held within a hollow cage attached to the plunger by a threaded retainer or end nut at the lower end of the plunger assembly. Thus, the valve reciprocates between an internal valve seat (valve closed) in a hollow space inside the cage and the inside surface of the lower end of the cage (valve open). A conventional clutch is appropriate for some applications, especially when its assembly is well controlled to produce uniform assemblies. Such a clutch may be formed of a bobbin split into two hemispherical halves and surrounded by one or two ordinary coil springs that function as a sort of garter to clamp the stem of the valve or dart between the two halves of the bobbin, thereby resisting the sliding motion of the stem within the bobbin. The clutch assembly is typically held in a fixed position within the cage. Each ‘garter’ spring is wrapped around its groove and the ends crimped together, typically in a hand operation that is subject to some variability in the tension around the bobbin halves and possible failure of the crimped joint, which could affect the reliability of the clutch when in a downhole environment.
While generally effective in lifting accumulated fluids and gas of unproductive wells such conventional bypass plungers tend to be complex and suffer from reliability problems in an environment that subjects them to high impact forces, very caustic fluids, elevated temperatures and the like. Various ways have been attempted to simplify construction of bypass plungers, improve their reliability and performance, and to reduce the cost of manufacture. However, failures remain common, and a substantial need exists to eliminate the causes of these failures. What is needed is a bypass plunger design that solves the structural problems with existing designs and provides a more reliable and efficient performance in the downhole environment.